Constructing travel itineraries from tagged geo-temporal photographs

ABSTRACT

One embodiment accesses two or more photos taken by one or more travelers at one or more destinations and one or more points-of-interest located within the destinations; constructs one or more photo streams for each unique traveler-destination combination, wherein each one of the photo streams comprises two or more of the photos taken by the corresponding traveler at the corresponding destination; maps each one of the photos to one of the points-of-interest; constructs one or more timed paths for each unique traveler-destination combination based on the photo streams and the mapping between the photos and the points-of-interest, wherein each one of the timed paths comprises one or more of the points-of-interest located within the corresponding destination and visited by the corresponding travel; and constructs an itinerary based on a start point-of-interest, an end point-of-interest, a time constraint, and the timed paths.

TECHNICAL FIELD

The present disclosure generally relates to constructing travelitineraries.

BACKGROUND

For any traveler traveling to any destination, the traveler or someoneconnected with the traveler typically plan and prepare an itinerary forthe trip. However, travel itinerary planning is often a difficult andtime consuming task, especially for a traveler visiting a destinationfor the first time. Often, planning a travel itinerary involvessubstantial research to identify points-of-interest (POIs) at thedestination worth visiting, the time worth spending at each POI, and thetime it may take to travel from one POI to another POI. Without anyprior knowledge, one must rely on travel books, personal travel blogs,or a combination of online resources and services such as travel guides,map services, public transportation sites, and human intelligence topiece together an itinerary.

All these options have shortcomings. Travel books do not cover allcities and locations and, perhaps more importantly, are not free.Personal travel blogs reflect individual person's view, with noguarantees provided over the writer's experience or the amount ofpreparation invested in planning the trip. Finally, compiling anitinerary by selecting individual POIs and researching their to's andfro's is a task that is both time consuming and requires significantresearch expertise.

SUMMARY

The present disclosure generally relates to constructing travelitineraries.

Particular embodiments access two or more photos, wherein each one ofthe photos is associated with a location and a time at which the photois taken, and taken by one of one or more travelers while visiting oneof one or more destinations, and one or more points-of-interest, whereineach one of the points-of-interest is located within one of thedestinations. Particular embodiments construct one or more photo streamsfor each unique traveler-destination combination, wherein each one ofthe photo streams comprises two or more of the photos taken by thecorresponding traveler at the corresponding destination and orderedaccording to the respective times at which the photos are taken.Particular embodiments map each one of the photos to one of thepoints-of-interest. Particular embodiments construct one or more timedpaths for each unique traveler-destination combination based on thephoto streams and the mapping between the photos and thepoints-of-interest, wherein each one of the timed paths comprises one ormore of the points-of-interest located within the correspondingdestination, for each one of the points-of-interest located within thecorresponding destination, a visit time representing a first amount oftime the corresponding traveler spends at the point-of-interest, and foreach one of one or more pairs of points-of-interest located within thecorresponding destination, a transit time representing a second amountof time it takes the corresponding traveler to travel from a first oneof the pair of points-of-interest to a second one of the pair ofpoints-of-interest. Particular embodiments construct an itinerary basedon a start point-of-interest, an end point-of-interest, a timeconstraint, and the timed paths.

These and other features, aspects, and advantages of the disclosure aredescribed in more detail below in the detailed description and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example method of constructing travel itinerariesfrom tagged geo-temporal photographs.

FIG. 2A illustrates an example set of photos.

FIG. 2B illustrates four example photo streams for an exampledestination.

FIG. 2C illustrates an example mapping between photos andpoints-of-interest.

FIG. 2D illustrates four example timed paths.

FIG. 3 illustrates an example network environment.

FIG. 4 illustrates an example computer system.

DETAILED DESCRIPTION

The present disclosure is now described in detail with reference to afew embodiments thereof as illustrated in the accompanying drawings. Inthe following description, numerous specific details are set forth inorder to provide a thorough understanding of the present disclosure. Itis apparent, however, to one skilled in the art, that the presentdisclosure may be practiced without some or all of these specificdetails. In other instances, well known process steps and/or structureshave not been described in detail in order not to unnecessarily obscurethe present disclosure. In addition, while the disclosure is describedin conjunction with the particular embodiments, it should be understoodthat this description is not intended to limit the disclosure to thedescribed embodiments. To the contrary, the description is intended tocover alternatives, modifications, and equivalents as may be includedwithin the spirit and scope of the disclosure as defined by the appendedclaims.

With the advancement of digital photography and the rapid rise of richmedia sharing sites such as Flickr (http://www.flickr.com/) and Picasa™Web Albums (http://picasaweb.google.com), millions of travelers are nowsharing their travel experiences through rich media data such asphotographs. More interestingly, users are increasingly associatingshared media with rich contextual information. Flickr photos, forexample, are usually time-stamped by the date and time of when they weretaken. Furthermore, they are often tagged with geographical information(e.g., latitudes and longitudes) on where the photos were taken, whichmay be mapped to specific POIs. Even more frequently, the photos areassociated with textual metadata such as tags, titles, notes, anddescriptions. Such shared photos may be seen as billions of geo-temporalbreadcrumbs that may promisingly serve as a latent source reflecting thetrips of millions of travelers.

Particular embodiments may take advantage of the rich informationprovided by these shared photos together with their associated metadataand automatically construct travel itineraries, and more importantly,travel itineraries at a large scale, from these breadcrumbs (i.e., theinformation that may be extracted from the photos and their metadata).For example, by analyzing these breadcrumbs associated with a traveler'sphoto stream, particular embodiments may deduce the cities visited bythe traveler, which POIs that traveler took photos at, how long thattraveler spent at each POI, and what the transit time was between POIsvisited in succession. By aggregating such timed paths of manytravelers, particular embodiments may construct itineraries that reflectthe “wisdom” of the touring crowds. Each such itinerary may be comprisedof a sequence of POIs, with recommended visit times and approximatetransit times between them.

FIG. 1 illustrates an example method of constructing travel itinerariesfrom tagged geo-temporal photographs. The steps illustrated in FIG. 1are described in connection with FIG. 2. Particular embodiments maycollect a set of photos from any applicable sources (step 110). Asindicated above, people often share their travel photos at variouswebsites, such as Flickr. Particular embodiments may collect the set ofphotos from these websites. Particular embodiments may combine photosshared at multiple websites to form the set so that the number of photosin the set is sufficient large and thus reflecting the experiences ofmany travelers. FIG. 2A illustrates an example set of photos 210.

In particular embodiments, for any trip, there may be one or moredestinations. A destination may be, for example and without limitation,a country, a state, a county, a city, a national park, or a mountainrange. Within each destination there may be one or more POIs. A POI maybe, for example and without limitation, a park, a museum, a monument, azoo, a natural site, a historical site, a religious site, or a shoppingarea. Particular embodiments contemplate any applicable types ofdestinations and POIs. To simplify the discussion, FIG. 1 is describedusing cities as an example type for destinations. Thus, there may be oneor more POIs within each city. However, the same concept may be appliedto any type of destination.

For clarification purposes, hereafter, let P={p₁, p₂, . . . , p_(n1)}denote a set of photos, U={u₁, u₂, . . . , u_(n2)} denote the owners(also referred to as users) of the photos, and C={c₁, c₂, . . . ,c_(n3)} denote a set of cities, which is used as an example set ofdestinations, where n1, n2, and n3 may be any positive integer. Notethat a user or an owner may also be a traveler who has taken the photos,and thus, in the context of the present disclosure, the terms “user”,“owner”, and “traveler” may be used interchangeably. In particularembodiments, each photo pεP may be described by one or more attributes.For example and without limitation, for a given p, u^(P) may identifythe owner of p; tt^(P) and tu^(P) may indicate when p was taken andshared on a website (e.g., Flickr), respectively (i.e., temporalinformation); lat^(p) and long^(p), if available, may indicate where interms of latitude and longitude p was taken (e.g., geographical or geoinformation); and {θ₁ ^(p), θ₂ ^(p), . . . , θ_(n4) ^(p)}, where n4 maybe any positive integer, may be the set of tags associated with p. Forexample, a photo of the Eiffel Tower in Paris may be tagged with “TourEiffel, Eiffel Tower, Architecture, Paris, Travel”. In particularembodiments, each city cεC may have a set of POIs, denoted as L^(c)={l₁,l₂, . . . , l_(n5)}, where n5 may be any positive integer. In particularembodiments, each POI lεL^(c) may be described by one or moreattributes. For example and without limitation, name^(l) may uniquelyidentify l; City^(l) is the city to which l belong (i.e., the citywithin which l is located); lat^(l) and long^(l) are the latitude andlongitude of l.

Sometimes, a website (e.g., Flickr) may allow its users to organizetheir photos into photo-sets, where each photo-set may include one ormore related photos. Often, users may group travel-related photos intosuch photo-sets, with each photo-set devoted to a particular trip ordestination. In addition, users may associate descriptive tags to aphoto-set. In particular embodiments, the tags associated with aphoto-set are propagated to all the photos within the photo-set.

Given these fundamental concepts, particular embodiments may constructphoto streams for individual destinations from the set of photos (step120). In particular embodiments, for each destination (e.g., a city),one or more photo streams may be constructed from the set of photos(e.g., set of photos 210). In particular embodiments, a photo stream mayinclude one or more photos of the same destination and taken by the sametourist during the same trip and arranged in the order of the time thatthese photos were taken. In particular embodiments, photos of differentdestinations, from different trips, or taken by different tourists formdifferent photo streams. Of course, people often travel in groups. It isnot uncommon that several people (e.g., friends or families) may travelto a destination together, and at the destination, they may in turn takephotos of each other or for each other. When they return home, oneperson may upload all the photos of the trip to a website, regardless ofwhich person actually has taken which photo. As a result, all the photosmay appear to be associated with this person. For the purpose of thepresent disclosure, particular embodiments may assume that the personwho has posted a photo is the person who has taken the photo.

FIG. 2B illustrates four example photo streams 222, 224, 226, 228 for aparticular city (e.g., San Francisco). For example, photo stream 222includes three photos that may be taken by a first tourist during avisit to San Francisco. The first photo in photo stream 222 is takenbefore the second photo in photo stream 222, which is taken before thethird photo in photo stream 222. Photo stream 224 includes four photosthat may be taken by a second tourist during a visit to San Francisco.Photo stream 226 includes three photos that may be taken by a thirdtourist during a visit to San Francisco. Of course, a particular touristmay visit a particular destination multiple times and taken photosduring each trip. Suppose the first tourist has visited San Franciscotwice. Photo stream 228 includes five photos that may be taken by thefirst tourist during his second visit to San Francisco. Similarly, aparticular tourist may visit multiple destinations during a single trip.Suppose the second tourist has visited San Francisco and Los Angelesduring a single trip. The photos the second tourist has taken in SanFrancisco form photo stream 224. The photos the second tourist has takenin Los Angles form another, separate photo stream (not illustrated inFIG. 2B).

When constructing photo streams for any given destination, particularembodiments may consider several issues. For example, particularembodiments may need to identify, from the set of photos, thoseindividual photos that are associated with the destination and are ownedby tourists. Conversely, particular embodiments my need to pruneirrelevant photos that are not associated with the destination or notowned by tourists. For example, given a city, c, pruning away irrelevantphotos may involve several tasks. First, particular embodiments mayidentify, from the set of photos, those individual photos that arelikely to be taken within the city. Second, particular embodiments mayidentify, from the owners of the photos, those owners who are likely tobe tourists visiting the city, as opposed to, for example, residents ofthe city. Third, particular embodiments may remove, from those photosthat have identified as likely being taken within the city, the photoswhose stored photo-taken time may be inaccurate.

To identify the photos of the city, C, particular embodiments mayleverage the semantic tags associated with the individual photos.Particular embodiments may collect a set of names of the city, includingits proper name and various popular variants, denoted as Name^(c).Particular embodiments may use the following RULE 1 to associated photoswith the city as follows.

RULE 1 (Photo-City Association). A photo p is associated with the city cif p's set of tags, including any tags propagated from the photo-set towhich p belongs, contains at least one tag matching any name variant inName^(c).

For example, New York City may be referred to as “New York”, “NYC”,“Manhattan”, “the big apple”, etc., which collectively form Name^(c) forNew York City. Any photo whose tags include one of these name variantsis considered to be associated with New York City. Note that particularembodiments do not tap the geo information of the photos at this stage,as experiments indicate that it does not significantly improve thecity-photo association and yet may be far more costly to compute. Ofcourse, alternative embodiments may use the geo information of thephotos to determine in which city the photos have been taken.

To distinguish tourists visiting a city and residents of the city,particular embodiments may rely on the observation that, with respect toPOIs, city residents often exhibit different visiting patterns fromtypical tourists. For example, city residents usually are not underpressure to visit many POIs within a time constraint. Thus, travelitineraries generated from patterns derived from residents are notlikely to be useful for tourists. To address this problem, particularembodiments may adopt the technique described in Leveraging ExplicitlyDisclosed Location Information to Understand Touristic Dynamics: a CaseStudy, by Fabien Girardin, Filippo Dal Fiore, Carlo Ratti, and JosepBlat, Journal of Location-Based Services, 2 (1):41-54, 2008. Particularembodiments may implement the following heuristic RULE 2:

RULE 2 (Tourist User). A user u (i.e., a owner of one or more photos) isconsidered as a tourist of the city c, if the span of the photo-takentimes between u's first and last photos in c is no more than n days.That is, u is considered as a tourist visiting c if the first phototaken by u in c and the last photo taken by u in c is no more than ndays apart.

Particular embodiments may determine the value of n based onexperiments. For example, n may be empirically set to 21. The assumptionhere is that while most tourists concentrate their visits within a shorttime period from several days to a couple of weeks, residents will takepictures of the city over a much longer period of time. Particularembodiments may also enforce that a user visits at least two POIs of cto be considered as a tourist. In particular embodiments, once a user uis identified as a non-tourist to a city c, all of u's photos associatedwith C may be eliminated for the purpose of constructing photo streamsfor c.

Constructing itineraries with accurate predictions of visit and transittimes requires the photos to have reliable timestamps, which, inparticular embodiments, may be verified by the following RULE 3.

RULE 3 (Accurate Photo-taken time). A photo p is considered to have anaccurate photo-taken time tt^(p) if its minutes and seconds aredifferent from those of its upload time tu^(p). Particular embodimentsmay require both timestamps to be at the resolution of 1 second.Moreover, if the minutes and seconds of tt^(p) and tu^(p) do match, p isconsidered to have an accurate photo-taken time, if tt^(p) and tu^(p)are more than 24 hours apart.

Intuitively, differences in the seconds or minutes of tt^(p) and tu^(p)eliminate the possibility that the photo-taken time tt^(p) is set bydefault to the up-load time tu^(p), which is a practice adopted by somemedia sharing websites (e.g., Flickr) whenever the photo-taken timeinformation is missing. The 24 hour rule may be used to recover photosmistakenly eliminated in the first round (i.e., according to the firstpart of RULE 3) due to, for example, the time zone differences. Inparticular embodiments, if a photo does not have an accurate photo-takentime according to RULE 3, it is ignored for the rest of the process.

Particular embodiments may then group all photos that satisfy all threerules by owner-destination or owner-trip-destination, and within eachunique combination of owner-trip-destination, sort the photos accordingtheir photo-taken times. The result is a collection of photo streamsS^(u,t,c), one for each unique combination of owner, trip, anddestination.

As indicated above, each photo stream includes photos of a particulardestination, taken by a particular tourist, during a particular trip.Typically, during each trip, a tourist may take successive photos ofvarious POIs at a destination, and as described in more detail below,metadata associated with the photos in each photo stream may be used toextract information concerning how much time the tourist has spent ateach POI (i.e., visiting time of a POI) and how much time it has takenthe tourist to travel from one POI to another POI (i.e., transit timebetween two POIs). During a particular trip, a tourist may spendmultiple days at the same destination, visiting multiple POIs (e.g., afew POIs each day). At the end of each day, the tourist may return tohis temporary lodging at the destination (e.g., a hotel) and rest. Whilethe tourist returns to his hotel to rest each night, it is unlikely thatthe tourist has taken any photo while sleeping. Thus, there may be a gapin time between the last photo taken during a first day and the firstphoto taken during a second day. To avoid this time gap being mistakenlyconstrued as the transit time between the last POI the tourist hasvisited during the first day and the first POI the tourist has visitedduring the second day, particular embodiments may examine the gapbetween the photo-taken time of the photos within each photo stream, andif there is a sufficiently long gap between two successive photos (e.g.,more than 8 hours, 12 hours, 24 hours, or 48 hours), particularembodiments may divide the photo streams into two separate photostreams.

For those photos that have been identified as associated withdestinations and owned by tourists, particular embodiments may map themto the POIs of the destinations (step 130). Particular embodiments may,for each destination, extract its POIs and associate individual photoswith the POIs (i.e., photo-POI association). FIG. 2C illustrates severalexample photos mapped to several example POIs. Typically, each photo 232may be mapped to one POI 234, and several photos 232 may be mapped tothe same POI 234.

The POIs of a destination may be extracted from various sources, andparticular embodiments contemplate any applicable sources. For example,many websites, such as Yahoo! Travel (http://travel.yahoo.com) or LonelyPlanet (http://travel.lonelyplanet.com), list attractions and POIs formany cities. Particular embodiments may rely on these websites toextract the set of popular land-marks, attractions, tourist sites, etc.,collectively as a set of POIs, L^(c), for a given city. Furthermore,particular embodiments may employ the publicly available Yahoo! Maps API(http://developer.yahoo.com/maps) to extract the geo-locations (e.g.,latitudes and longitudes) of these POIs. Geo-locations are returned whenquerying the Yahoo! Maps API with the names of the POIs.

Given geo information of the POIs, there may be alternative methods tomap a photo to a particular POI, including geo-based or tag-basedmethods. The geo-based mapping relies on matching the photo's geolocation to the POI's geo location; and the tag-based mapping relies onmatching the photo's tags to the names of the POIs. Intuitively, thegeo-based mapping may be a more desirable method, especially for largeand distinctive POIs that are often photographed from afar (e.g., theGolden Gate Bridge in San Francisco). Otherwise, particular embodimentsmay associate a photo with the POI appearing in its textual tags, evenwhen the photo was actually taken from far away. This may be misleadingwhen computing the visit and transit times of that POI.

If a photo has geo information, particular embodiments may associate ageo-located photo p to a POI lεL^(c) whenever l is the POI closest to p,and p was taken within distance δ of l. For example, δ may be set to 100meters. Unfortunately, not all photos have associated geo information.Thus, if a photo does not have geo information, particular embodimentsmay apply tag-based matching as a secondary measure. Given a photo tagand the name of a POI, particular embodiments may compute the similaritybetween the two based on their trigram set similarity. Particularembodiments thus associate a photo p to a lεL^(c) whenever l has thehighest similarity with any tag of p among all the POIs in L^(c).Particular embodiments may require that the similarity satisfy athreshold requirement.

The overall POI association process, according to particularembodiments, is depicted in ALGORITHM 1. It augments the previouslyidentified individual photo streams S^(u,t,c) with associated POIinformation to produce the POI photo stream, S^(u,t,c,l).

ALGORITHM 1: Associating Photos with POIs Require: city-relevant photostreams S^(u,t,c) ; a city c ; 1: L^(c) = getPOIs( c ); 2: for (p ∈S^(u,t,c) ) do 3: for (l ∈ L^(c) ) do 4: if (geoMap( p , l ) ∥ tagMap((p , l )) then 5: associate(( p , l ); 6: end if 7: end for 8: end for 9:return photo streams with photos associated with city POIs

Particular embodiments may construct timed paths among the POIs (step140). In particular embodiments, each timed path may include one or morePOIs and the visit time for each POI and the transit time for each pairof POIs. The visit time for a POI may be the average time a tourist mayspend visiting the POI. The transit time for a pair of POIs may be theaverage time it takes a tourist to travel from one POI to the other POI.

A timed path may be represented graphically. FIG. 2D illustrates fourexample timed paths 242, 244, 246, 248. For each timed path, the nodesrepresent the POIs, and each node is associated with an average visittime. Two nodes (i.e., two POIs) may be connected with an edge, which isassociated with an average transit time.

From step 120, for a given tourist (i.e., user), trip, and destination(e.g., city), all the photos may be arranged according to theirphoto-taken time to form a photo stream. However, the informationprovided by such photo streams may not be readily useful, as within aphoto stream, successive (i.e., adjacent) photos may have been taken ondifferent days, and thus their corresponding POIs may have been visitedby the user on different days. To address this issue, particularembodiments may segment each photo stream into sub-streams using asimple heuristic: the photo stream may be split whenever the timedifference between two successive photos, tt^(p) ^(i+1) −tt^(p) ^(i) ,is greater than some threshold τ. For example, based on experiments, τmay be set to 8 hours. Consequently, if a photo stream contains twosuccessive photos that are more than τ apart, the photo stream issegmented into two sub-streams. In particular embodiments, eachsub-stream containing only photos from a single POI or containing lessthan η number of photos (e.g., η=3) may be discarded as such sub-streamscannot reliably contribute to the computation of visit and transittimes. The remaining sub-streams may then be used to construct the timedpaths.

In constructing timed paths particular embodiments may rely on thenotion of a timed visit, defined as follows.

DEFINITION 1 (Timed Visit). Let lεL^(c) be a POI of a city c. A timedvisit at l is the triplet (l, t^(s), t^(e)), where t^(s) is the starttime at l, t^(e) is the end time at l, and t^(e)≧t^(s).

Particular embodiments may construct timed visits at l from maximalsubsequences of photos associated with l in a photo stream or a photosub-stream. The photo-taken time stamp of the first photo associatedwith l in the subsequence determines t^(s), while that of the last photoassociated with l in the subsequence determines t^(e). A timed visitimplies a lower bound on the actual time spent by the particular user atthat POI, since the start and end times represent the earliest time andthe latest time that a photo was taken at the POI, and not the actualtimes of arrival at and departure from the POI.

Particular embodiments may define a timed path as follows.

DEFINITION 2 (Timed Path). A sequence of timed visits, TP^(c)={(l₁, t₁^(s), t₁ ^(e)), . . . , (l_(k), t_(k) ^(s), t_(k) ^(e))} is called atimed path for city c whenever t_(j) ^(e)<t_(j+1) ^(s) for j=1, . . . ,k−1. The difference t_(j+1) ^(s)−t_(j) ^(e) is called the transit timefrom l_(j) to l_(j+1).

In particular embodiments, timed paths are induced by the sequence oftimed visits derived from a photo stream or sub-stream. Transit timesimply an upper bound on the time it took for the particular user to movefrom one POI to another POI. The following ALGORITHM 2 illustrates thegeneration of timed paths according to particular embodiments.

ALGORITHM 2: Generating Timed Paths Require: POI-associated photostreams S^(u,t,c,l) ; a city; a time threshold τ ; 1: for (s ∈S^(u,t,c,l) ) do 2: SS = segmentStream( s , τ ) 3: for (ss ∈ SS ) do 4:pruneNonTourists( ss ) 5: addPaths(TP^(c) , ss) 6: end for 7: end for 8:return timed paths TP^(c)

Given a start POI at a destination, an end POI at the destination, and atime constraint (i.e., the total time to be spent at the destination),particular embodiments may automatically construct an itinerary usingthe timed paths (step 150). The start POI, end POI, and time constraintmay be specified by a traveler or there may be default start POI, endPOI, and time constraint for a particular destination. Given the set oftimed paths, the goal, in particular embodiments, is to aggregate theactions of many individual travelers into coherent itineraries whiletaking into consideration POI popularity. To this effect, particularembodiments may define a full undirected graph G^(c)=(V=L^(c),E=L^(c)×L^(c)) on which the following predicates are defined:

In particular embodiments, P(lεL^(c)) is the popularity of each POI l inL^(c) (i.e., the number of distinct users who visited l). In particularembodiments, POIs visited by less than 10 users may be removed.

In particular embodiments, T(lεL^(c)) is the visit time at each POI l inL^(c). Different people may stay for different durations at a POI formany reasons, some of which transcend the value of the landmark itself(e.g. they may stop for a meal there). Moreover, a single user may visita POI multiple times, each with a different visit time. Particularembodiments may take the longest visit of each user u at a POI as u'svisit time and set T(lεL^(c)) to be the visit time closest to, forexample the 75th percentile among all users. This heuristic may overcomemuch of the noise and compensates for the fact that the visit timesmeasured are only lower bounds on the real visit times.

In particular embodiments, E(eεE) is the median or average transit timebetween each pair of L^(c) POIs in L^(c). Each timed path may contributemultiple transit times between the same pair of points. The median oraverage, then, is calculated over the set of all transit times collectedfrom all timed paths. In particular embodiments, edges with a single (orno) transit in the data may be assigned a transit time of infinity. Morespecifically, in particular embodiments, the transmit time between eachpair of POIs may be calculated using a two-step process. First, for eachpair of POIs and each traveler, the median or average transmit timebetween the two POIs may be calculated for the individual traveler. Notethat a traveler may travel between the same two POIs multiple times.Second, for each pair of POIs, the median or average transmit timebetween the two POIs may be calculated for all the travelers. For eachpair of POIs, the final median or average transmit time obtained fromthe two-step calculation may be used as the transmit time between thetwo POIs.

In particular embodiments, V(lεL^(c)) is the prize or value that anitinerary gets from visiting each POI l in L^(c), which may be afunction of the popularity and visit duration of l. The dependency onthe visit duration is required, in particular embodiments, to preventbias towards POIs with short visit durations. Particular embodiments mayset the prize to be the product of the popularity and the visitduration.

Note that while theoretically, transit times should obey the triangleinequality, this may not be the case with the transit times empiricallycollected. To overcome this difficulty and enforce the triangleinequality, particular embodiments may apply metric completion on G^(c).The drawback of metric completion, in some cases, is that an erroneous(short) transit duration at one edge can propagate to many other edges.Filtering nodes may reduce the effect of this drawback. To furtherreduce it, particular embodiments may ignore transit times of edges forwhich fewer than a certain number of transitions, X, were recorded.

In particular embodiments, an itinerary is a path in the graph G^(c),where a node (i.e., POI) in the path may be visited more than once. LetI be an itinerary; its prize V(I) may be defined as the sum of prizes ofthe unique set of POIs (i.e., a POI's prize is counted only once even ifit is visited multiple times) along the path (i.e., the itinerary). Thetime T(I) of the itinerary is the sum of visit times to the unique setof POIs along the path, plus the transit times along all edges on thepath, including those that are traversed more than once. The intuitionbehind counting prize and visit time only once for POIs visited multipletimes is that one might pass through a POI several times, always payingthe transit time, but spending visit time there to view the place onlyonce. However, since G^(c) satisfies the triangle inequality, particularembodiments may assume without loss of generality that an itinerary is asimple path. Under this assumption, T(I) becomes the sum of visit timesof its nodes plus the transit times of its edges.

Given the definitions above, particular embodiments may formulate theItinerary Mining Problem (IMP) as follows.

Instance: A graph G=(L^(C), E) with edge costs (=transit times){T(e)|eεE} obeying the triangle inequality, (time) budget B, node prizes{V(l)|lεL^(c)}, node costs (=visit times) {T(l)|lεL^(c)}, and two nodess,tεL^(c).

Objective: Find an itinerary in G from s to t of cost (=time) at most Bmaximizing total node prizes.

The Itinerary Mining Problem is NP-Hard, which may be proved by areduction from the Hamiltonian Path problem. Note that IMP is closelyrelated to the well-studied, NP-Hard Orienteering problem. In theOrienteering problem there are only edge costs (no node costs), and itsclassic formulation is over undirected graphs. A common extension of theOrienteering problem specifies a time window for visiting each node. Anode v, then, contributes to the prize collected by a path only if thepath reaches v within its time window. Time windows help modelrecommended visit times of POIs. In this regard, there is anincomparable approximation ratio of

$O\left( {\max\left\{ {{\log\;{OPT}},{\log\frac{L_{\max}}{L_{{mi}n}}}} \right\}} \right)$for Orienteering with time windows, where L_(min) and L_(max) are thelengths of the shortest and longest time windows, respectively.Moreover, an O(log² n)-approximation algorithm for Orienteering withtime windows is described in Improved Algorithms for Orienteering andRelated Problems, by Chandra Chekuri and Nitish Korula, SODA, pages661-670, 2008.

Typically, the above algorithms all have large time complexity, inpractice, O(n⁸) or worse. In a different approach, a quasi-polynomialrecursive greedy approximation algorithm may be used for Orienteering,whose approximation ratio is ┌log k┐+1, where k is the length of theoptimal path in terms of nodes. This approximation ratio is appealing inthe present context, as a reasonable itinerary is expected to visit onlya relatively few POIs each day. By imposing an upper bound k on k, thetime complexity of the algorithm may be reduced to O((2+nA logB)^(log k) ) Moreover, the algorithm is highly extensible.

As mentioned above, the major difference between IMP and theOrienteering problem is that IMP includes node costs. Hence particularembodiments may reduce IMP to the directed Orienteering problem byadding T(l) to the cost of each edge entering l. The idea of therecursive greedy algorithm is to guess the middle node v of the path andthe amount of prize collected by the path in the first half (i.e., up tonode v). The algorithm then determines how much budget has to beinvested in the first half to collect the guessed prize, and callsitself recursively on both halves of the path. The second call is notallowed to use the nodes that belong to the first half of the pathreturned by the first call.

An extension of the recursive greedy algorithm for Orienteering (RG-QP)allows it to produce multi-day, or more specifically, multi-part,itineraries. The idea is to supply the algorithm with multiple tripletscomprised of start-point (i.e., start POI), end-point (i.e., end POI),and time allowance (i.e., time constraint). Each triplet represents a“part” and corresponds to the parameters s, t and B of the IMPformulation above. Typically, the end-point of triplet j would be thestart point of triplet j+1, representing the location where a touristmay spend a night. In a multi-day stay in a city, those may all be thetourist's hotel. In particular embodiments, a multi-day itinerary isconsidered valid if it is the concatenation of sub-itineraries thatconnect the source and destination nodes of the triplets whilerespecting the corresponding time allowance.

A limitation of this approach for automatically constructing itinerariesfor road trips, as opposed to multi-day city stays, may be the need tospecify as input to the algorithm the “layover points”. Particularembodiments may either mine recommended layover spots from user data, orto have the algorithm reach “eligible layovers” at certain intervals(e.g., every 9-10 trip hours).

Although FIG. 1 has been described with respect to photographs as aspecific example of geo-temporally tagged rich media objects, the sameconcept may be applied to any kind of geo-temporally tagged rich mediaobjects. A set of such objects may be obtained from any suitablesources, whether public or private.

Particular embodiments may be implemented in a network environment. FIG.3 illustrates an example network environment 300. Network environment300 includes a network 310 coupling one or more servers 320 and one ormore clients 330 to each other. In particular embodiments, network 310is an intranet, an extranet, a virtual private network (VPN), a localarea network (LAN), a wireless LAN (WLAN), a wide area network (WAN), ametropolitan area network (MAN), a communications network, a satellitenetwork, a portion of the Internet, or another network 310 or acombination of two or more such networks 310. The present disclosurecontemplates any suitable network 310.

One or more links 350 couple servers 320 or clients 330 to network 310.In particular embodiments, one or more links 350 each includes one ormore wired, wireless, or optical links 350. In particular embodiments,one or more links 350 each includes an intranet, an extranet, a VPN, aLAN, a WLAN, a WAN, a MAN, a communications network, a satellitenetwork, a portion of the Internet, or another link 350 or a combinationof two or more such links 350. The present disclosure contemplates anysuitable links 350 coupling servers 320 and clients 330 to network 310.

In particular embodiments, each server 320 may be a unitary server ormay be a distributed server spanning multiple computers or multipledatacenters. Servers 320 may be of various types, such as, for exampleand without limitation, web server, news server, mail server, messageserver, advertising server, file server, application server, exchangeserver, database server, or proxy server. In particular embodiments,each server 320 may include hardware, software, or embedded logiccomponents or a combination of two or more such components for carryingout the appropriate functionalities implemented or supported by server320. For example, a web server is generally capable of hosting websitescontaining web pages or particular elements of web pages. Morespecifically, a web server may host HTML files or other file types, ormay dynamically create or constitute files upon a request, andcommunicate them to clients 330 in response to HTTP or other requestsfrom clients 330. A mail server is generally capable of providingelectronic mail services to various clients 330. A database server isgenerally capable of providing an interface for managing data stored inone or more data stores.

In particular embodiments, each client 330 may be an electronic deviceincluding hardware, software, or embedded logic components or acombination of two or more such components and capable of carrying outthe appropriate functionalities implemented or supported by client 330.For example and without limitation, a client 330 may be a desktopcomputer system, a notebook computer system, a netbook computer system,a handheld electronic device, or a mobile telephone. A client 330 mayenable an network user at client 330 to access network 310. A client 330may have a web browser, such as Microsoft Internet Explorer or MozillaFirefox, and may have one or more add-ons, plug-ins, or otherextensions, such as Google Toolbar or Yahoo Toolbar. A client 330 mayenable its user to communicate with other users at other clients 330.The present disclosure contemplates any suitable clients 330.

In particular embodiments, one or more data storages 340 may becommunicatively linked to one or more servers 320 via one or more links350. In particular embodiments, data storages 340 may be used to storevarious types of information. In particular embodiments, the informationstored in data storages 340 may be organized according to specific datastructures. Particular embodiments may provide interfaces that enableservers 320 or clients 330 to manage (e.g., retrieve, modify, add, ordelete) the information stored in data storage 340. In particularembodiments, the photos may be stored in data storage 340.

Particular embodiments may be implemented on one or more computersystems. FIG. 4 illustrates an example computer system 400. Inparticular embodiments, one or more computer systems 400 perform one ormore steps of one or more methods described or illustrated herein. Inparticular embodiments, one or more computer systems 400 providefunctionality described or illustrated herein. In particularembodiments, software running on one or more computer systems 400performs one or more steps of one or more methods described orillustrated herein or provides functionality described or illustratedherein. Particular embodiments include one or more portions of one ormore computer systems 400.

This disclosure contemplates any suitable number of computer systems400. This disclosure contemplates computer system 400 taking anysuitable physical form. As example and not by way of limitation,computer system 400 may be an embedded computer system, a system-on-chip(SOC), a single-board computer system (SBC) (such as, for example, acomputer-on-module (COM) or system-on-module (SOM)), a desktop computersystem, a laptop or notebook computer system, an interactive kiosk, amainframe, a mesh of computer systems, a mobile telephone, a personaldigital assistant (PDA), a server, or a combination of two or more ofthese. Where appropriate, computer system 400 may include one or morecomputer systems 400; be unitary or distributed; span multiplelocations; span multiple machines; or reside in a cloud, which mayinclude one or more cloud components in one or more networks. Whereappropriate, one or more computer systems 400 may perform withoutsubstantial spatial or temporal limitation one or more steps of one ormore methods described or illustrated herein. As an example and not byway of limitation, one or more computer systems 400 may perform in realtime or in batch mode one or more steps of one or more methods describedor illustrated herein. One or more computer systems 400 may perform atdifferent times or at different locations one or more steps of one ormore methods described or illustrated herein, where appropriate.

In particular embodiments, computer system 400 includes a processor 402,memory 404, storage 406, an input/output (I/O) interface 408, acommunication interface 410, and a bus 412. Although this disclosuredescribes and illustrates a particular computer system having aparticular number of particular components in a particular arrangement,this disclosure contemplates any suitable computer system having anysuitable number of any suitable components in any suitable arrangement.

In particular embodiments, processor 402 includes hardware for executinginstructions, such as those making up a computer program. As an exampleand not by way of limitation, to execute instructions, processor 402 mayretrieve (or fetch) the instructions from an internal register, aninternal cache, memory 404, or storage 406; decode and execute them; andthen write one or more results to an internal register, an internalcache, memory 404, or storage 406. In particular embodiments, processor402 may include one or more internal caches for data, instructions, oraddresses. The present disclosure contemplates processor 402 includingany suitable number of any suitable internal caches, where appropriate.As an example and not by way of limitation, processor 402 may includeone or more instruction caches, one or more data caches, and one or moretranslation lookaside buffers (TLBs). Instructions in the instructioncaches may be copies of instructions in memory 404 or storage 406, andthe instruction caches may speed up retrieval of those instructions byprocessor 402. Data in the data caches may be copies of data in memory404 or storage 406 for instructions executing at processor 402 tooperate on; the results of previous instructions executed at processor402 for access by subsequent instructions executing at processor 402 orfor writing to memory 404 or storage 406; or other suitable data. Thedata caches may speed up read or write operations by processor 402. TheTLBs may speed up virtual-address translation for processor 402. Inparticular embodiments, processor 402 may include one or more internalregisters for data, instructions, or addresses. The present disclosurecontemplates processor 402 including any suitable number of any suitableinternal registers, where appropriate. Where appropriate, processor 402may include one or more arithmetic logic units (ALUs); be a multi-coreprocessor; or include one or more processors 402. Although thisdisclosure describes and illustrates a particular processor, thisdisclosure contemplates any suitable processor.

In particular embodiments, memory 404 includes main memory for storinginstructions for processor 402 to execute or data for processor 402 tooperate on. As an example and not by way of limitation, computer system400 may load instructions from storage 406 or another source (such as,for example, another computer system 400) to memory 404. Processor 402may then load the instructions from memory 404 to an internal registeror internal cache. To execute the instructions, processor 402 mayretrieve the instructions from the internal register or internal cacheand decode them. During or after execution of the instructions,processor 402 may write one or more results (which may be intermediateor final results) to the internal register or internal cache. Processor402 may then write one or more of those results to memory 404. Inparticular embodiments, processor 402 executes only instructions in oneor more internal registers or internal caches or in memory 404 (asopposed to storage 406 or elsewhere) and operates only on data in one ormore internal registers or internal caches or in memory 404 (as opposedto storage 406 or elsewhere). One or more memory buses (which may eachinclude an address bus and a data bus) may couple processor 402 tomemory 404. Bus 412 may include one or more memory buses, as describedbelow. In particular embodiments, one or more memory management units(MMUs) reside between processor 402 and memory 404 and facilitateaccesses to memory 404 requested by processor 402. In particularembodiments, memory 404 includes random access memory (RAM). This RAMmay be volatile memory, where appropriate Where appropriate, this RAMmay be dynamic RAM (DRAM) or static RAM (SRAM). Moreover, whereappropriate, this RAM may be single-ported or multi-ported RAM. Thepresent disclosure contemplates any suitable RAM. Memory 404 may includeone or more memories 404, where appropriate. Although this disclosuredescribes and illustrates particular memory, this disclosurecontemplates any suitable memory.

In particular embodiments, storage 406 includes mass storage for data orinstructions. As an example and not by way of limitation, storage 406may include an HDD, a floppy disk drive, flash memory, an optical disc,a magneto-optical disc, magnetic tape, or a Universal Serial Bus (USB)drive or a combination of two or more of these. Storage 406 may includeremovable or non-removable (or fixed) media, where appropriate. Storage406 may be internal or external to computer system 400, whereappropriate. In particular embodiments, storage 406 is non-volatile,solid-state memory. In particular embodiments, storage 406 includesread-only memory (ROM). Where appropriate, this ROM may bemask-programmed ROM, programmable ROM (PROM), erasable PROM (EPROM),electrically erasable PROM (EEPROM), electrically alterable ROM (EAROM),or flash memory or a combination of two or more of these. Thisdisclosure contemplates mass storage 406 taking any suitable physicalform. Storage 406 may include one or more storage control unitsfacilitating communication between processor 402 and storage 406, whereappropriate. Where appropriate, storage 406 may include one or morestorages 406. Although this disclosure describes and illustratesparticular storage, this disclosure contemplates any suitable storage.

In particular embodiments, I/O interface 408 includes hardware,software, or both providing one or more interfaces for communicationbetween computer system 400 and one or more I/O devices. Computer system400 may include one or more of these I/O devices, where appropriate. Oneor more of these I/O devices may enable communication between a personand computer system 400. As an example and not by way of limitation, anI/O device may include a keyboard, keypad, microphone, monitor, mouse,printer, scanner, speaker, still camera, stylus, tablet, touchscreen,trackball, video camera, another suitable I/O device or a combination oftwo or more of these. An I/O device may include one or more sensors.This disclosure contemplates any suitable I/O devices and any suitableI/O interfaces 408 for them. Where appropriate, I/O interface 408 mayinclude one or more device or software drivers enabling processor 402 todrive one or more of these I/O devices. I/O interface 408 may includeone or more I/O interfaces 408, where appropriate. Although thisdisclosure describes and illustrates a particular I/O interface, thisdisclosure contemplates any suitable I/O interface.

In particular embodiments, communication interface 410 includeshardware, software, or both providing one or more interfaces forcommunication (such as, for example, packet-based communication) betweencomputer system 400 and one or more other computer systems 400 or one ormore networks. As an example and not by way of limitation, communicationinterface 410 may include a network interface controller (NIC) ornetwork adapter for communicating with an Ethernet or other wire-basednetwork or a wireless NIC (WNIC) or wireless adapter for communicatingwith a wireless network, such as a WI-FI network. This disclosurecontemplates any suitable network and any suitable communicationinterface 410 for it. As an example and not by way of limitation,computer system 400 may communicate with an ad hoc network, a personalarea network (PAN), a local area network (LAN), a wide area network(WAN), a metropolitan area network (MAN), or one or more portions of theInternet or a combination of two or more of these. One or more portionsof one or more of these networks may be wired or wireless. As anexample, computer system 400 may communicate with a wireless PAN (WPAN)(such as, for example, a BLUETOOTH WPAN), a WI-FI network, a WI-MAXnetwork, a cellular telephone network (such as, for example, a GlobalSystem for Mobile Communications (GSM) network), or other suitablewireless network or a combination of two or more of these. Computersystem 400 may include any suitable communication interface 410 for anyof these networks, where appropriate. Communication interface 410 mayinclude one or more communication interfaces 410, where appropriate.Although this disclosure describes and illustrates a particularcommunication interface, this disclosure contemplates any suitablecommunication interface.

In particular embodiments, bus 412 includes hardware, software, or bothcoupling components of computer system 400 to each other. As an exampleand not by way of limitation, bus 412 may include an AcceleratedGraphics Port (AGP) or other graphics bus, an Enhanced Industry StandardArchitecture (EISA) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT)interconnect, an Industry Standard Architecture (ISA) bus, an INFINIBANDinterconnect, a low-pin-count (LPC) bus, a memory bus, a Micro ChannelArchitecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, aPCI-Express (PCI-X) bus, a serial advanced technology attachment (SATA)bus, a Video Electronics Standards Association local (VLB) bus, oranother suitable bus or a combination of two or more of these. Bus 412may include one or more buses 412, where appropriate. Although thisdisclosure describes and illustrates a particular bus, this disclosurecontemplates any suitable bus or interconnect.

Herein, reference to a computer-readable storage medium encompasses oneor more non-transitory, tangible computer-readable storage mediapossessing structure. As an example and not by way of limitation, acomputer-readable storage medium may include a semiconductor-based orother integrated circuit (IC) (such, as for example, afield-programmable gate array (FPGA) or an application-specific IC(ASIC)), a hard disk, an HDD, a hybrid hard drive (HHD), an opticaldisc, an optical disc drive (ODD), a magneto-optical disc, amagneto-optical drive, a floppy disk, a floppy disk drive (FDD),magnetic tape, a holographic storage medium, a solid-state drive (SSD),a RAM-drive, a SECURE DIGITAL card, a SECURE DIGITAL drive, or anothersuitable computer-readable storage medium or a combination of two ormore of these, where appropriate. Herein, reference to acomputer-readable storage medium excludes any medium that is noteligible for patent protection under 35 U.S.C. §101. Herein, referenceto a computer-readable storage medium excludes transitory forms ofsignal transmission (such as a propagating electrical or electromagneticsignal per se) to the extent that they are not eligible for patentprotection under 35 U.S.C. §101.

This disclosure contemplates one or more computer-readable storage mediaimplementing any suitable storage. In particular embodiments, acomputer-readable storage medium implements one or more portions ofprocessor 402 (such as, for example, one or more internal registers orcaches), one or more portions of memory 404, one or more portions ofstorage 406, or a combination of these, where appropriate. In particularembodiments, a computer-readable storage medium implements RAM or ROM.In particular embodiments, a computer-readable storage medium implementsvolatile or persistent memory. In particular embodiments, one or morecomputer-readable storage media embody software. Herein, reference tosoftware may encompass one or more applications, bytecode, one or morecomputer programs, one or more executables, one or more instructions,logic, machine code, one or more scripts, or source code, and viceversa, where appropriate. In particular embodiments, software includesone or more application programming interfaces (APIs). This disclosurecontemplates any suitable software written or otherwise expressed in anysuitable programming language or combination of programming languages.In particular embodiments, software is expressed as source code orobject code. In particular embodiments, software is expressed in ahigher-level programming language, such as, for example, C, Perl, or asuitable extension thereof. In particular embodiments, software isexpressed in a lower-level programming language, such as assemblylanguage (or machine code). In particular embodiments, software isexpressed in JAVA. In particular embodiments, software is expressed inHyper Text Markup Language (HTML), Extensible Markup Language (XML), orother suitable markup language.

The present disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsherein that a person having ordinary skill in the art would comprehend.Similarly, where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend.

1. A method comprising, by one or more computing devices: accessing: twoor more photos, wherein each one of the photos is associated with alocation and a time at which the photo is taken, and is taken by one ofone or more travelers while visiting one of one or more destinations,and one or more points-of-interest, wherein each one of thepoints-of-interest is located within one of the destinations;constructing one or more photo streams for each uniquetraveler-destination combination, wherein each one of the photo streamscomprises two or more of the photos taken by the corresponding travelerat the corresponding destination and ordered according to the respectivetimes at which the photos are taken; mapping each one of the photos toone of the points-of-interest; constructing one or more timed paths foreach unique traveler-destination combination based on the photo streamsand the mapping between the photos and the points-of-interest, whereineach one of the timed paths comprises: one or more of thepoints-of-interest located within the corresponding destination, foreach one of the points-of-interest located within the correspondingdestination, a visit time representing a first amount of time thecorresponding traveler spends at the point-of-interest, and for each oneof one or more pairs of points-of-interest located within thecorresponding destination, a transit time representing a second amountof time it takes the corresponding traveler to travel from a first oneof the pair of points-of-interest to a second one of the pair ofpoints-of-interest; and constructing an itinerary based on a startpoint-of-interest, an end point-of-interest, a time constraint, and thetimed paths.
 2. The method recited in claim 1, further comprising, foreach one of the photo streams, between any two successive photos, if adifference between a first time at which a first one of the twosuccessive photos is taken and a second time at which a second one ofthe two successive photos is taken is greater than a predeterminedthreshold, then dividing the photo stream into two new photo streams,replacing the old photo stream, wherein the first one of the two newphoto streams comprises from a first photo to the first one of the twosuccessive photos of the old photo stream, and the second one of the twonew photo streams comprises from the second one of the two successivephotos to a last photo of the old photo stream.
 3. The method recited inclaim 1, wherein for each one of the timed paths constructed for eachtraveler-destination combination: the points-of-interest are orderedaccording to a sequence of the corresponding traveler visiting thepoints-of-interest, for each one of the points-of-interest, the visittime is a difference between a first time a first photo is taken inconnection with the point-of-interest and a second time a last photo istaken in connection with the point-of-interest based on the photostreams constructed for the traveler-destination combination, and foreach one of the pairs of points-of-interest, the transit time is adifference between a third time a last photo is taken in connection withthe first one of the pair of points-of-interest and a fourth time afirst photo is taken in connection with the second one of the pair ofpoints-of-interest based on the photo streams constructed for thetraveler-destination combination.
 4. The method recited in claim 1,wherein: each one of the points-of-interest is associated with a valuedetermined base on popularity and visit duration of thepoint-of-interest, and the additional points-of-interest of theitinerary are selected to maximize a total value of thepoints-of-interest of the itinerary.
 5. The method recited in claim 1,wherein: the itinerary comprises the start point-of-interest, the endpoint-of-interest, zero or more additional points-of-interest in-betweenthe start point-of-interest and the end point-of-interest, and a totalamount of time needed to visit the start point-of-interest, theadditional points-of-interest, and the end point-of-interest satisfiesthe time constraint.
 6. The method recited in claim 5, wherein: thestart point-of-interest, the additional points-of-interest, and the endpoint-of-interest are located within a same one of the destinations, andthe total amount of time of the itinerary comprises the visit times ofall the points-of-interest of the itinerary and the transmit timesbetween all pairs of successive points-of-interest of the itinerary. 7.A system, comprising: a memory comprising instructions executable by oneor more processors; and one or more processors coupled to the memory andoperable to execute the instructions, the one or more processors beingoperable when executing the instructions to: access: two or more photos,wherein each one of the photos is associated with a location and a timeat which the photo is taken, and is taken by one of one or moretravelers while visiting one of one or more destinations, and one ormore points-of-interest, wherein each one of the points-of-interest islocated within one of the destinations; construct one or more photostreams for each unique traveler-destination combination, wherein eachone of the photo streams comprises two or more of the photos taken bythe corresponding traveler at the corresponding destination and orderedaccording to the respective times at which the photos are taken; mapeach one of the photos to one of the points-of-interest; construct oneor more timed paths for each unique traveler-destination combinationbased on the photo streams and the mapping between the photos and thepoints-of-interest, wherein each one of the timed paths comprises: oneor more of the points-of-interest located within the correspondingdestination, for each one of the points-of-interest located within thecorresponding destination, a visit time representing a first amount oftime the corresponding traveler spends at the point-of-interest, and foreach one of one or more pairs of points-of-interest located within thecorresponding destination, a transit time representing a second amountof time it takes the corresponding traveler to travel from a first oneof the pair of points-of-interest to a second one of the pair ofpoints-of-interest; and construct an itinerary based on a startpoint-of-interest, an end point-of-interest, a time constraint, and thetimed paths.
 8. The system recited in claim 7, wherein the one or moreprocessors are further operable when executing the instructions to, foreach one of the photo streams, between any two successive photos, if adifference between a first time at which a first one of the twosuccessive photos is taken and a second time at which a second one ofthe two successive photos is taken is greater than a predeterminedthreshold, then divide the photo stream into two new photo streams,replacing the old photo stream, wherein the first one of the two newphoto streams comprises from a first photo to the first one of the twosuccessive photos of the old photo stream, and the second one of the twonew photo streams comprises from the second one of the two successivephotos to a last photo of the old photo stream.
 9. The system recited inclaim 7, wherein for each one of the timed paths constructed for eachtraveler-destination combination: the points-of-interest are orderedaccording to a sequence of the corresponding traveler visiting thepoints-of-interest, for each one of the points-of-interest, the visittime is a difference between a first time a first photo is taken inconnection with the point-of-interest and a second time a last photo istaken in connection with the point-of-interest based on the photostreams constructed for the traveler-destination combination, and foreach one of the pairs of points-of-interest, the transit time is adifference between a third time a last photo is taken in connection withthe first one of the pair of points-of-interest and a fourth time afirst photo is taken in connection with the second one of the pair ofpoints-of-interest based on the photo streams constructed for thetraveler-destination combination.
 10. The system recited in claim 7,wherein: each one of the points-of-interest is associated with a valuedetermined base on popularity and visit duration of thepoint-of-interest, and the additional points-of-interest of theitinerary are selected to maximize a total value of thepoints-of-interest of the itinerary.
 11. The system recited in claim 7,wherein: the itinerary comprises the start point-of-interest, the endpoint-of-interest, zero or more additional points-of-interest in-betweenthe start point-of-interest and the end point-of-interest, and a totalamount of time needed to visit the start point-of-interest, theadditional points-of-interest, and the end point-of-interest satisfiesthe time constraint.
 12. The system recited in claim 11, wherein: thestart point-of-interest, the additional points-of-interest, and the endpoint-of-interest are located within a same one of the destinations, andthe total amount of time of the itinerary comprises the visit times ofall the points-of-interest of the itinerary and the transmit timesbetween all pairs of successive points-of-interest of the itinerary. 13.One or more computer-readable tangible storage media embodying softwareoperable when executed by one or more computer systems to: access: twoor more photos, wherein each one of the photos is associated with alocation and a time at which the photo is taken, and is taken by one ofone or more travelers while visiting one of one or more destinations,and one or more points-of-interest, wherein each one of thepoints-of-interest is located within one of the destinations; constructone or more photo streams for each unique traveler-destinationcombination, wherein each one of the photo streams comprises two or moreof the photos taken by the corresponding traveler at the correspondingdestination and ordered according to the respective times at which thephotos are taken; map each one of the photos to one of thepoints-of-interest; construct one or more timed paths for each uniquetraveler-destination combination based on the photo streams and themapping between the photos and the points-of-interest, wherein each oneof the timed paths comprises: one or more of the points-of-interestlocated within the corresponding destination, for each one of thepoints-of-interest located within the corresponding destination, a visittime representing a first amount of time the corresponding travelerspends at the point-of-interest, and for each one of one or more pairsof points-of-interest located within the corresponding destination, atransit time representing a second amount of time it takes thecorresponding traveler to travel from a first one of the pair ofpoints-of-interest to a second one of the pair of points-of-interest;and construct an itinerary based on a start point-of-interest, an endpoint-of-interest, a time constraint, and the timed paths.
 14. The mediarecited in claim 13, wherein the software is further operable whenexecuted by the one or more computer systems to, for each one of thephoto streams, between any two successive photos, if a differencebetween a first time at which a first one of the two successive photosis taken and a second time at which a second one of the two successivephotos is taken is greater than a predetermined threshold, then dividethe photo stream into two new photo streams, replacing the old photostream, wherein the first one of the two new photo streams comprisesfrom a first photo to the first one of the two successive photos of theold photo stream, and the second one of the two new photo streamscomprises from the second one of the two successive photos to a lastphoto of the old photo stream.
 15. The media recited in claim 13,wherein for each one of the timed paths constructed for eachtraveler-destination combination: the points-of-interest are orderedaccording to a sequence of the corresponding traveler visiting thepoints-of-interest, for each one of the points-of-interest, the visittime is a difference between a first time a first photo is taken inconnection with the point-of-interest and a second time a last photo istaken in connection with the point-of-interest based on the photostreams constructed for the traveler-destination combination, and foreach one of the pairs of points-of-interest, the transit time is adifference between a third time a last photo is taken in connection withthe first one of the pair of points-of-interest and a fourth time afirst photo is taken in connection with the second one of the pair ofpoints-of-interest based on the photo streams constructed for thetraveler-destination combination.
 16. The media recited in claim 13,wherein: each one of the points-of-interest is associated with a valuedetermined base on popularity and visit duration of thepoint-of-interest, and the additional points-of-interest of theitinerary are selected to maximize a total value of thepoints-of-interest of the itinerary.
 17. The media recited in claim 13,wherein: the itinerary comprises the start point-of-interest, the endpoint-of-interest, zero or more additional points-of-interest in-betweenthe start point-of-interest and the end point-of-interest, and a totalamount of time needed to visit the start point-of-interest, theadditional points-of-interest, and the end point-of-interest satisfiesthe time constraint.
 18. The media recited in claim 17, wherein: thestart point-of-interest, the additional points-of-interest, and the endpoint-of-interest are located within a same one of the destinations, andthe total amount of time of the itinerary comprises the visit times ofall the points-of-interest of the itinerary and the transmit timesbetween all pairs of successive points-of-interest of the itinerary.